Diabetes and other retinal vascular diseases are a major cause of unavoidable vision loss. The retinal vasculature also has a unique role in helping to understand how systemic diseases such as diabetes and hypertension are damaging other vasculature in the body which may not be as readily accessible to noninvasive measures as the retina. Recently we have shown that adaptive optics imaging of the retinal vessels allows precise quantification of blood flow and vascular structure. We are able to image individual cells within the walls of the retinal vasculature, measure the relation between vascular lumens and vascular walls in vessels as small as 10 microns, and can measure blood flow changes in response to visual stimuli smaller than 2 degrees of visual extent. The current proposal will combine measures of both the overall structure of the microvasculature (including the wall to lumen ratio) and fine structure (cellular composition), with measurements of blood velocity, based on our ability to image individual erythrocytes as they move through the blood vessels). By providing visual stimuli we will look at the neurovascular coupling and develop techniques to look at how local regions regulate flow as well as whether impairment of neurovascular coupling is local or global. By combing measurements over space we will measure network changes in the vascular tree and how structure is related to blood velocity. We will also perform a limited longitudinal study to examine how capillary dropout and anomalous vascular structures spread, as well as how local blood flow is altered in the presence of local ischemia and vascular alterations. We will also extend our capabilities to identify capillary wall components using programmable aperture microscopy (PAM). This will extend our adaptive optics based techniques for darkfield imaging of the retina to allow us to image and quantify the cells of even the smallest retinal capillaries in vivo. This combination of measurements will allow us to look at how aging, diabetes and hypertension cause local changes to the vasculature, and in turn how vascular changes alter the delivery of blood to the retina locally. The unique advantage of this cellular imaging approach to vascular disease in humans is that it fills a much needed link between current clinical measures and animal studies. The long term goal is to provide a deeper understanding of why some patients do better than others and to provide a quantitative estimate of the prognosis for severe vascular complications based on an individual's own vasculature. Such ability would allow more specific treatments, ultimately decreasing the cost of health care. Since the vasculature of the retina has the potential to act as a biomarker for advanced microvascular disease in other parts of the body such tools would also be of help in managing the systemic complications of diabetes and hypertension.